This application relates generally to gas turbine engine rotor assemblies and, more particularly, to methods and apparatus for mounting a removable turbine blade to a turbine disk.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor to generate hot combustion gases. The hot combustion gases are directed to one or more turbines, wherein energy is extracted. A gas turbine includes at least one row of circumferentially spaced rotor blades.
Gas turbine engine rotor blades include airfoils having leading and trailing edges, a pressure side, and a suction side. The pressure and suction sides connect at the airfoil leading and trailing edges, and extend radially from a rotor blade platform. Each rotor blade also includes a dovetail radially inward from the platform, which facilitates mounting the rotor blade to the rotor disk.
Each gas turbine rotor disk includes a plurality of dovetail slots to facilitate coupling the rotor blades to the rotor disk. Each dovetail slot includes disk fillets, disk pressure faces and disk relief faces. Rotor blade dovetails are received within the rotor disk dovetail slots such that the rotor blades extend radially outward from the rotor disk.
The dovetail is generally complementary to the dovetail slot and mate together form a dovetail assembly. The dovetail includes at least one pair of tangs that mount into dovetail slot disk fillets. The dovetail tangs include blade pressure faces which oppose the disk pressure faces, and blade relief faces which oppose the disk relief faces. To accommodate conflicting design factors, at least some known dovetail assemblies include a relief gap extending between opposed relief faces when opposed pressure faces are engaged.
In operation, typically the turbine is rotated by combustion gases. Occasionally, when combustion within the engine is terminated, atmospheric air passing through the engine will rotate the turbine at a significantly reduced rate. Such a condition is referred to as xe2x80x9cwindmillingxe2x80x9d. Reduced centrifugal forces are generated during windmilling, allowing blade pressure faces to disengage from disk pressure faces. The dovetail moves such that the blade relief faces engage the disk relief faces. The dovetail movement also forms a pressure face gap between blade pressure faces and disk pressure faces. The movement of the rotor blade may produce an audible noise, including noise from benign contact between a platform downstream wing and a forward portion of a stage two nozzle while windmilling. Continued operation with a pressure face gap may result in the entry of dirt or foreign material between the opposed pressure faces, which may cause misalignment of the rotor blade and brinelling of the pressure faces.
In an exemplary embodiment, a dovetail assembly includes non-parallel relief faces that facilitate reducing pressure face brinelling in gas turbine engines. The dovetail assembly includes a plurality of rotor blades including dovetails. Each dovetail includes at least a pair of blade tangs that include blade relief faces. The dovetail assembly also includes a rotor disk that includes a plurality of dovetail slots sized to receive the dovetails. Each dovetail slot is defined by at least one pair of opposing disk tangs including disk relief faces. The dovetail assembly is configured such that when the dovetail is coupled to the rotor disk, the disk relief faces are non-parallel to the blade relief faces.
In another aspect of the invention, a method for fabricating a rotor disk for a gas turbine engine facilitates reducing radial movement of the rotor blade. The rotor disk includes a dovetail slot defined by at least one pair of disk tangs. The rotor blade includes a dovetail including at least one pair of blade tangs. The method includes the steps of forming a blade pressure face on at least one blade tang and forming a disk pressure face on at least one disk tang such that the disk pressure face is substantially parallel to the blade pressure face when the rotor blade is mounted in the rotor disk. The method further includes the steps of forming a blade relief face on at least one blade tang and forming a disk relief face on at least one disk tang such that the disk relief face is substantially non-parallel to the blade relief face when the rotor blade is mounted in the rotor disk and the disk pressure face engages the blade pressure face. As a result, the blade and disk relief faces form a reduced relief gap which facilitates limiting the entry of foreign material between the pressure faces during turbine windmilling and reducing noise resulting from rotor blade drop.